1. Field of the Invention
The present invention relates to a disc drive apparatus which records/reproduces information signals on or from an optical disc such as an optical disc or a magneto-optical disc.
2. Description of the Related Art
As an optical disc, an optical disc such as a CD (Compact Disc) and a DVD (Digital Versatile Disc), a magneto-optical disc such as an MD (Mini Disc), and the like are widely known, and various disc drive apparatuses have accordingly been launched on the market.
As shown in, for example, FIG. 13, a disc drive unit 200 included in the disc drive apparatus which records/reproduces information signals on or from an optical disc comprises: a disc rotation drive mechanism 201 which rotatively drives the optical disc; an optical pick-up 202 which performs writing/reading operation of signals on or from the optical disc rotatively driven by the disc rotation drive mechanism 201; and a pick-up feeding mechanism 203 which feeds the optical pick-up 202 in the radial direction of the optical disc. Each of the above components is attached to a base 204 to constitute the disc drive unit 200.
The disc rotation drive mechanism 201 has a flat-shaped spindle motor 206 on which a turntable 205 for holding the optical disc is provided. The spindle motor 206 rotatively drives the optical disc and turntable 205 as a unit.
The optical pick-up 202 allows an objective lens 207 to focus a light beam emitted from a semiconductor laser onto a signal recording surface of the optical disc, and detects a return light beam reflected from the signal recording surface of the optical disc by means of a photodetector, thereby performing writing/reading operation on or from the optical disc.
The pick-up feeding mechanism 203 has: a pair of guide shafts 208a and 208b which movably support the optical pick-up 202 in the radial direction of the optical disc; a rack member 209 attached to the optical pick-up 202; a lead screw 210 engaged with the rack member 209; and an stepping motor 211 which rotatively drives the lead screw 210. The stepping motor 211 rotatively drives the lead screw 210 to drive/displace the rack member 209 engaged with the lead screw 210 and the optical pick-up 202 as a unit in the radial direction of the optical disc.
An opening portion for turntable 212a and an opening portion for optical pick-up 212b are continuously formed inside the base 204 so as to allow the turntable 205 and the optical pick-up 202 to face upward, respectively. The spindle motor 206, both end portions of each of the pair of guide shafts 208a and 208b, lead screw 210, stepping motor 211 and the like are attached to one main surface on the side opposite to the other main surface on which the opening portions 212a and 212b are formed to allow the turntable 205 and the optical pick-up 202 to face upward, respectively.
In the disc drive unit 200 having the above configuration, the disc rotation drive mechanism 201 rotatively drives the optical disc and the pick-up feeding mechanism 203 feeds the optical pick-up 202 in the radial direction of the optical disc. In parallel with the above operations, the optical pick-up 202 performs writing/reading operation of signals with respect to the optical disc, thereby recording/reproducing information signals on or from a desired recording track of the optical disc.
In the above disc drive unit 200, several approaches are made in order to meet the growth of a recording density of the optical disc. For example, wavelength of the light beam emitted from the optical pick-up 202 and irradiated on the optical disc is shortened, or numerical aperture of the objective lens 207 is increased. However, this generates tilt (hereinafter referred to as “skew”) of an optical axis of the light beam emitted from the optical pick-up 202 with respect to a signal recording surface of the optical disc to increase frequency in occurrence of aberration, thereby leading to significant deterioration in recording/reproduction characteristics. That is, in the disc drive unit 200, the more responses to the growth of a recording density are made, the smaller a tolerance of skew becomes. Therefore, it is necessary that the light beam emitted from the optical pick-up 202 strike a signal recording surface of the optical disc held by the turntable 205 at right angles in order to obtain satisfactory recording/reproducing characteristics with respect to the optical disc.
To adjust skew of the optical pick-up 202 relative to the optical disc, two methods are available; one is a method of adjusting attachment angle of the spindle motor 206 relative to the base 204, and the other is a method of adjusting skew of the pair of the guide shafts 208a and 208b supporting the optical pick-up 202 (refer to, for example, Jpn. Pat. Appln. Laid-Open Publication No. 2002-171709).
When the disc drive apparatus is mounted in a portable electronic device such as a notebook personal computer as an ultraslim disc drive apparatus, it will be subjected to various restraints in the aforementioned skew adjustment of the optical pick-up 202 relative to the optical disc.
For example, in the ultraslim disc drive apparatus, a clearance in the vertical direction of the optical disc held by the turntable 205 is very small. Therefore, in the aforementioned method of adjusting attachment angle of the spindle motor 206 relative to the base 204, the outer peripheral side of the optical disc held by the turntable 205 greatly tilts. This increases the risk of a crash between the optical disc and the optical pick-up 202 at the outer peripheral side of the optical disc when an external impact is applied to the disc drive unit 200. Especially, a reduction in the thickness of the entire apparatus to 9.5 mm, which corresponds to the thickness of a hard disc drive (HDD) unit not only increases the risk of a crash between the optical disc and the optical pick-up 202, but also greatly narrows the range for skew adjustment. Further, in a method of adjusting skew of both the spindle motor 206 and the pair of the guide shafts 208a and 208b, increased adjustment points complicate an adjustment work or positioning calculation, which makes it difficult to obtain accuracy.
Therefore, in a type that requires a reduction in size, weight, and thickness, e.g., a type in which the disc drive unit 200 is directly attached to a disc tray, the following method is desirable. That is, in a state where the spindle motor 206 is fixed to the base 204 and parallelism between the base 204 and turntable 205 which holds the optical disc is maintained, positions that support each end portions of the pair of guide shafts 208a and 208b are adjusted so that the light beam emitted from the optical pick-up 202 strikes a signal recording surface of the optical disc at right angles to thereby adjust the distance between the optical pick-up 202 and a signal recording surface of the optical disc, and skew of the optical pick-up 202 relative to a signal recording surface of the optical disc.
From the viewpoint of the aforementioned case, when the spindle motor 206 is attached to the base 204, parallelism between the turntable 205 which holds the optical disc and the base 204 must be maintained with high level of accuracy.
As shown in FIG. 14, in the above disc drive unit 200, a support plate 213 which supports the spindle motor 206 is attached to the back surface of the base 204 through three locating members 214a, 214b, and 214c. 
For maintaining parallelism between the base 204 and the turntable 205, the three locating members 214a, 214b, and 214c are designed such that abutment surfaces 215a, 215b, and 215c that come in contact with the support plate 213 have the same height dimension D′. A boss 216 for locating the support plate 213 in the in-plane direction is formed at a central potion of each of the abutment surfaces 215a, 215b, and 215c so as to project from the abutment surfaces. Each of the bosses 216 has a screw hole 217 formed at a central portion thereof to screw on the support plate 213. On the other hand, three boss holes 218 corresponding to the locating members 214a, 214b, and 214c are formed on the support plate 213. That is, with the bosses 216 of the locating members 214a, 214b, and 214c engaged respectively with the boss holes 218 of the support plate 213, the support plate 213 supporting the spindle motor 206 is fixed to the base 204 through the locating members 214a, 214b, and 214c by inserting screws 219 respectively into the screw holes 218 of the bosses 216 that face the boss holes 218 respectively.
In the conventional configuration in which the spindle motor 206 supported by the support plate 213 is fixed to the base 204 through the three locating members 214a, 214b, and 214c, even when the three locating members 214a, 214b, and 214c are designed such that abutment surfaces 215a, 215b, and 215c that come in contact with the support plate 213 have the same height dimension D′, as shown in FIG. 15, a dimension deviation of up to 2d′ occurs depending on the difference between the dimensional tolerances ±d′ of each of the locating members 214a, 214b, and 214c. 
As a result, in the above conventional attachment configuration of the spindle motor 206, skew, wobble or the like is caused between the turntable 205 and the base 204 due to the difference between the dimensional tolerances ±d′ of each of the locating members 214a, 214b, and 214c, which makes it very difficult to maintain parallelism between the base 204 and the optical disc held by the turntable 205. Further, to prevent the skew from occurring when the spindle motor 206 is fixed to the base 204, it is necessary to increase dimensional accuracy in the vertical direction of each of the locating members 214a, 214b, and 214c. This results in an increase in the number of parts required, leading to an increase in manufacturing cost.